Actuators and valve assembly components may be operated or driven by devices such as handwheel assemblies. The rotation of a handwheel in either a clockwise or counter-clockwise direction imparts a rotational force on a drive shaft, which in turn, operates an actuator or valve assembly. For example, a handwheel device typically used to drive actuators and valve assemblies is illustrated in FIG. 1. Rotation of the handwheel drives a stem in or out of an actuator housing or valve assembly, thereby driving components contained therein. The use of handwheels and handwheel devices with actuators and valve assemblies is well known.
Actuators and valve assemblies driven by handwheels are typically subject to torque limitations. Application of torque beyond the torque limits of an actuator or valve assembly can damage the actuator or valve assembly. Once an excessive amount of torque has been applied to an actuator or a valve assembly, the device should be replaced.
To prevent damage caused by the excessive application of torque, warnings are usually printed in the user manuals that accompany the actuators or valve assemblies. In other instances, warnings may also be placed on actuator housings or on handwheels attached to an actuator in order to discourage an over-application of torque to the assembly. During operation, however, it is difficult, if not impossible, for an operator to monitor the amount of torque being applied to an actuator or valve assembly. This is especially true when an operator can only estimate the amount of torque that is being applied to a device based on their experience and on a feel for the amount of force that is being applied at any given time.
In many cases, there is no mechanism to prevent the application of an excessive amount of torque to an actuator or a valve assembly. More often than not, when excessive torque is applied to an actuator or valve assembly, the excessive torque causes damage to the actuator or valve assembly, resulting in the need for maintenance or replacement of the actuator or valve assembly. Therefore, it would be desirable to provide a mechanism by which an operator could be prevented from imparting an excessive amount of torque to an actuator or valve assembly by operation of a handwheel.
Although the application of excessive force and torque to an actuator or valve assembly is undesirable, emergency situations may arise which require such application. In those instances, the ability of an operator to override a mechanism preventing the application of an excessive amount of torque should not be hindered.
Furthermore, in many cases where damage to an actuator or valve assembly is caused by the application of excessive torque to a device, the manufacturer may be called upon to fix the device. The inability of the manufacturer to determine whether a device was damaged due to the application of an excessive amount of torque to the device or whether some other legitimate damage occurred is troublesome. Therefore, it is desirable to provide a mechanism by which manufacturers may monitor or determine when damage to an actuator or valve assembly has been caused by the application of excessive amounts of torque to the device rather than by a defect or normal wear-and-tear of the device.
Therefore, there is a need to provide a mechanism that limits the amount of torque applied to an actuator or valve assembly. It is also desirable to provide a mechanism for overriding or disengaging a torque limiting device so that excessive amounts of torque may be applied to an actuator or valve assembly if the need for such excessive torque is required. In addition, it is desirable to provide a mechanism that indicates when a torque limiting device has been disengaged or overridden.